Abstract

Members of the approximately 900 species of echinoids are found on the
floor of all seas, often in large numbers. Sea urchins dot coastal rocks,
sometimes causing considerable bioerosion, and heart urchins and sand
dollars form extensive beds in offshore sands and muds. Many sea urchins
are important herbivores (Lawrence, 1975; Lawrence and Sammarco, 1982;
Harrold and Pearse, 1987), while others are omnivores or feed on detritus
and debris. Moreover, echinoids have a long and rich fossil record, so that
their evolutionary history is relatively well known. Mortensen's (1928-1951)
monographic treatment of echinoids is among the most complete ever given
to a large group of marine invertebrates. Smith (1984) and others built upon
the accumulated knowledge of living and fossil echinoids to formulate
cladistic analyses of the group. General accounts of echinoids are found in Hyman (1955), Harvey (1956a), Moore (1966), Nichols (1969), Smith (1984),
Kier (1987), Lawrence (1987), and V.B. Pearse et al. (1987). Much of the
earlier literature on reproduction of echinoids is summarized by Hyman
(1955) and Boolootian (1966); additional references up to 1965 are given by
Holland and Holland (1969a), and Lawrence (1987) reviewed aspects of
hermaphroditism and brooding.